Acaba, Padalka and Revin were originally scheduled to launch on
March 29, but a botched pressure test
cracked their Soyuz crew capsule. The flight was pushed back
by a month and a half to allow enough time for Russian space
contractor RSC Energia to ready a new capsule for service.

Once aboard the space station, the three spaceflyers will bring
the orbiting lab back to its full complement of six occupants.
Their fellow Expedition 31 crewmembers — NASA's Don Pettit,
Dutchman Andre Kuipers and cosmonaut Oleg Kononenko — have had
the station to themselves since April 27.

Acaba, Padalka and Revin will live in orbit for the next four
months, eventually returning to Earth in mid-September, NASA
officials said. The three newcomers will all serve as flight
engineers under the command of Expedition 31 chief Kononenko.
[ Quiz:
The Reality of Life in Orbit ]

New space experiences

Acaba, 44, is a native of Inglewood, Calif., and is making his
second career spaceflight. He has been to the station once
before, on the
space shuttle Discovery's STS-119 mission in 2009. But he
returned to Earth after just 13 days on that flight, so
this will be a new experience for him.

"I'm looking forward to going from someone who worked for two
weeks in space as a shuttle crewmember to now living in space —
living and working in space — as a long-duration crewmember,"
Acaba told reporters earlier this year. "Personally, I think
it'll be a much different experience — instead of just a
whirlwind, 'let's get the job done' to, you know, 'now this is
your home.'"

Acaba is one of NASA's educator astronauts and taught high school
and middle school before joining NASA's astronaut ranks in 2004.

Padalka, 53, is a veteran spaceflyer making his third trip to the
International Space Station on the Expedition 31 flight. A father
of three from Krasnodar, Russia he has racked up a total of 585
days in Earth orbit.

Tonight's launch will mark Padalka's fourth career spaceflight,
making him the most seasoned spaceflyer aboard the Soyuz capsule.
In addition to his two International Space Station flights in
2004 and 2009, Padalka also flew to Russia's Mir space station in
a 198-day mission that spanned parts of 1998 and 1999.

Unlike Padalka and Acaba, tonight's launch will mark the first
trip to space for Revin.

"I'm really looking forward to the experience," Revin, 46, told
SPACE.com through an interpreter a few months ago, citing the
chance to do important work and be part of a talented team.

"From the emotional point of view, the emotional aspect, I'm
really excited about having the opportunity to study Earth and
all that surrounds it," he added. "And also, I'm looking forward
to communicating with children and with other people, because
this is a great opportunity, using the resources that the station
can provide, for communication."

Revin is a native of Moscow, Russia, and has one son with his
wife Irina. He joined Russia's Federal Space Agency as a test
cosmonaut in 1996.

A historic arrival

While a stay aboard the space station is doubtless always
exciting, the Expedition 31 crewmembers will be treated to a
historic event if all goes according to plan.

The California-based company SpaceX is planning to
launch its Dragon capsule on an unmanned demonstration flight
to the orbiting lab on May 19, to see if the vehicle is ready to
begin a series of 12 contracted robotic cargo missions for NASA.

If the misssion goes well, Dragon will be the first private
spacecraft ever to dock with the space station, and the first of
those 12 cargo runs could begin later this year.

You can follow SPACE.com senior writer Mike Wall on
Twitter:@michaeldwall.
Follow SPACE.com for the latest in space science and exploration
news on Twitter@Spacedotcom and
onFacebook.